Helen Branswell has a story about a battle being waged among virologists and occupational health specialists regarding how influenza is spread from person to person:
Later this week virologists, infection control specialists and occupational health experts from Canada, the U.S. and Britain will gather in Toronto to start trying to answer a question that is the source of a polarized debate among them.
How does influenza spread from one person to the next in hospitals? Is it mainly transmitted by hand-to-hand contact and virus-laced droplets sneezed or coughed from the respiratory tracts of the infected? Or do those expelled viruses hover in the air for longer periods and over greater distances than heavy droplets, making airborne transmission a factor in flu’s spread?
It may sound like a debate over how many viruses can dance on the head of a pin. But this is no esoteric exercise. The outcome could determine how many health-care workers will be well enough – or willing – to look after the rest of us when the next flu pandemic strikes. (Helen Branswell, Canadian Press)
The practical issue is being framed this way. If flu is “airborne” (meaning that the virus is in very tiny aerosol droplets and remains suspended in the air for extended periods), then health care workers should use so-called N95 respirators. If not, then surgical masks are adequate.
We think this is bad framing. N95 respirators need to be fitted properly if they are to protect health care workers. Anyone working in close quarters with influenza patients, for example, intubating them or sunctioning them or doing respiratory hygiene on them, should be wearing a properly fitted N95 respirator, whatever the predominant droplet size. A surgical mask won’t protect them. On the other hand, if the virus remains suspended and viable for long periods in the air, then an N95 mask would have to be worn nearly constantly and not just in the hospital. Even then it might not protect sufficiently, depending upon particle size and infectivity of the virus. Small particles have high surface area to volume ratios and dry out very rapidly, becoming even smaller. It is not inconceivable they could be predominantly submicron size. The best protection in those circumstances might be ultra violet light germicidal irradiation (UVGI).
In our view this is a more fruitful direction than arguing whether N95 masks should be worn by health care workers. N95s should be used by all health care workers performing procedures on influenza patients. It is an open question whether they should be used on open wards, hospital rooms or clinics where patients are being cared for. The masks are not meant to be reused, need to be properly fitted and are uncomfortable for many people. Their efficacy in the more general health care settings is unknown. However if providing these masks makes it more likely health care workers will show up for work, then efforts should be made to do so, but that is a different question. It is our opinion they are not useful for the general environment, although we cannot prove this one way or another.
UVGI should be investigated for area disinfection of health care facilities and possibly other public venues if very small particle aerosols are thought to be a significant mode of spread. UVGI requires further study, which we suggest be undertaken with some urgency. Meanwhile, the mask arguments seem more like rearranging the deck chairs on the Titanic.